A. Field of the Invention
The present invention relates to an insertion section of an endoscope adapted to be inserted into the body cavity, and more specifically, to a flexible tube for use in the insertion section.
B. Description of the Prior Art
A typical endoscope comprises a distal section, insertion section, and operating section. The distal section is formed with openings for a view window, illumination window, and instrument channel. The insertion section includes a flexible tube portion and a remote-controlled bending portion, while the operating section includes a bending mechanism portion and an eyepiece portion. The endoscope contains therein the instrument channel and an optical fiber bundle for observation. An operator can insert the distal section, along with the insertion section, into the body cavity, observe the affected part of a patient's body, and give necessary medical care.
Conventionally known are endoscopes which are adapted individually for observation of internal organs, such as the gullet, stomach, duodenum, small intestine, colon, etc. In endoscopes applied to the observation of the duodenum, small intestine, or colon, in particular, the insertion section is inserted deep into the body cavity. It has been confirmed clinically that the flexibility of the insertion section greatly influences the ease of insertion thereof, and hence, reduces the degree of pain suffered by the patient.
Stated in Japanese Utility Model Disclosure (Kokai) No. 56-101301, for example, is a prior art method of improving the ease of insertion of an insertion section, used in an endoscope, thereby reducing the pain experienced by the patient. A flexible tube is used in the insertion section, and it has a two-layer structure as part of its sheath. The distal portion of the flexible tube is relatively rigid, so that the insertion section can be easily inserted into the body cavity. In an endoscope flexible tube stated in Japanese Utility Model Disclosure (Kokai) No. 55-112505, moreover, the sheath of the tube has a two-layer structure, composed of soft and rigid layers. The thickness of the rigid layer reduces gradually from the operating-section to the distal end.
Thus, in the conventional endoscopic flexible tubes, all or part of the sheath has a two-layer structure, which improves the flexibility of the sheath. Accordingly, insertion of the insertion section is relatively easy, so that the patient suffers less pain when the endoscope is operated in his body. Nothing has been improved, however, with regard to the elasticity of the insertion section, which influences the ease of the insertion most. It is therefore relatively hard to insert the insertion section of the prior art endoscopes into the body cavity. In consequence, the patient cannot be fully protected from pain when he is subjected to an endoscopic diagnosis or examination.